Polycarbonates are transparent thermoplastic high-performance plastic materials with desirable mechanical, optical, thermal and electrical properties. However, polycarbonates have a disadvantage of poor chemical resistance and are required to have a higher level of impact strength for use in various applications.
Various proposals have been made to improve the mechanical properties of polycarbonates. As an example, blending of polycarbonates with other materials has been proposed. However, this approach can cause deterioration of transparency inherent to polycarbonates. In many actual cases, polycarbonates lose their transparency even when small amounts of rubbery impact modifiers are added.
There is also a growing demand for plastics with unique colors and appearances. Thus there is also a need to develop polycarbonates that control the transparency of polymer matrices and do not undergo deterioration of physical properties, such as transparency and impact resistance, despite the use of visual effect additives.
In addition, numerous studies have been conducted to overcome the limited chemical resistance of polycarbonate resins. These studies are based on the problem that when polycarbonate resins are used as exterior materials of electrical/electronic products, diluent solvents of coating materials permeate the polycarbonate resins during coating to cause deterioration of mechanical properties. In order to solve this problem, efforts have been made to improve the physical properties of polycarbonates by blending with other thermoplastic resins. Such technical attempts are advantageous in achieving improved chemical resistance of polycarbonates but fail to ensure impact resistance or transparency thereof.
For example, U.S. Pat. No. 4,188,314 discloses a shaped article with improved chemical resistance that includes a polycarbonate and a copolyester. However, sufficient impact strength of the shaped article cannot be obtained. U.S. Pat. No. 4,634,737 discloses a resin composition including a copolyester-carbonate containing from 25 to 90 mole % ester bonds and an olefin acrylate copolymer. This composition has improved chemical resistance but is very low in transparency.
A number of investigations into the use of siloxane monomers have been conducted to increase the chemical resistance and impact strength of polycarbonates. However, a major problem is that the combination of polycarbonates and siloxane monomers causes a considerable reduction in transparency, one of the greatest advantages of polycarbonates, due to lack of compatibility between the polycarbonates and the siloxane monomers.
Thus, there is still a need for a copolymer including carbonate units and siloxane units that has excellent melt flow and ductility characteristics while maintaining high transparency and low haze.